1. Field of the Invention
The present invention relates generally to techniques of assembling modular electronic equipment. More particularly, it relates to methods and apparatus for selectively mounting and securing card guides within electronic equipment.
2. Description of the Prior Art
Modular construction techniques are widely used to manufacture a variety of electronic equipment. For example, manufactures of computer equipment use modular construction techniques extensively. With modular techniques, a manufacturer can economically and expeditiously assemble several variations of an electronic device using different combinations of preassembled modular circuits. Additionally, vendors may routinely assemble electronic systems from basic units at a point of sale. Further, end users are usually capable of reconfiguring and/or upgrading modular electronic systems with little effort. In most instances, replacing and/or adding modular electronic circuits in a system requires no more than a simple screwdriver and minimal mechanical skill.
For instance, a conventional personal computer (PC) system generally comprises arrays of prefabricated electronic components mounted on printed circuit boards (PCBs), to form combinations of PCB assemblies. PC manufacturers typically mount a variety of PCB assemblies on a common chassis, along with other components, to form a basic but often incomplete version of a final PC system. Then, in response to a customer request for a particular model having specific capabilities, a manufacturer or vendor adds one or more PCB assemblies and other components to the basic version to produce the appropriate configuration for the model requested. Later, the customer may wish to personally augment the capabilities of or upgrade the PC system. In that case, the manufacturer could provide the customer with the appropriate option cards, which the customer would self-install.
More specifically, a PC, a peripheral device or other modular system usually contains a main circuit board assembly, called a motherboard, which typically comprises a relatively large PCB on which many of the device's main components mount. The motherboard normally mounts on a chassis, which often forms a part of an outer casing that encloses the system components. In addition, a basic system usually includes other components that mount on the chassis and connect to the motherboard. Finally, unused card connectors and supports, which are equipped to accept certain option cards to be installed at some future time, are also located in a basic system. These unused connectors and supports are ordinarily associated with special card guides that help installers insert option cards quickly and accurately in their proper locations within the system.
Manufacturers normally mount card guides on strong, rigid members, such as the walls of a sheetmetal chassis. One common card guide has a plastic body and resilient mounting lugs with barbs that protrude from the bottom surface of the body. When installing these card guides, an installer begins by drilling appropriate mounting holes at suitable locations on a rigid structure. Next, the installer aligns the card guide so that the mounting lugs mate with the drilled holes. Finally, the installer presses on the card guide or strikes the guide with a hammer or other tool until the lugs snap into the holes.
To enhance the physical construction of some modular equipment and further simplify the instillation of option cards, it has been suggested that some option cards be piggybacked on a motherboard. Consequently, efforts are underway to develop techniques for mounting card guides directly on a fully populated motherboard. Although prior art techniques for mounting card guides have served their intended purpose, they have proved to be unreliable when used to install card guides on the relatively thin, flexible and delicate structure of an ordinary motherboard. Thus, manufacturers have rejected proposals to use the conventional card guides and the installation techniques described above. Manufacturers have found that the insertion forces exerted on a motherboard, as a result of snapping the barbed mounting lugs into their mounting holes, frequently flex and damage etched conductors and other components located on an ordinary motherboard.